Salisbury Cathedral Flooding

Salisbury Cathedral FloodedThe strategic flooding and drainage study area – the historic Salisbury Cathedral estate area, has flooded on many occasions during the last 1000 years.

Salisbury Cathedral commissioned Wilsham Consulting review the evidence of flooding, the mechanisms of flooding, areas of high risk and identify a strategy and options for flood mitigation. They us, because we are one of the leading independent specialist Civil Engineering  Consultancies in the UK and needed considerable depth and width of experience in hydraulic evaluation and flood mitigation design.

flood mitigation design

Salisbury Cathedral Flooded

With climate change and increased obstructions to flow, the centre of Salisbury is currently at the highest risk of flooding in its history. Consultation with the Environment Agency and evaluation of their proposals and studies, led to the conclusion that no effective mitigation measures within the catchment above Salisbury were likely to effectively reduce the risk in the foreseeable future.

The cost of flooding both in financial damage to historic structures and human impact is considerable. The availability of funds for flood mitigation is minimal. The report’s  proposals were therefore based on optimising flood mitigation benefit to the community with realistically available funds, as a community, rather than lengthy and unfocused Authority led project.

The report has concluded that doing nothing or awaiting full protection from a traditional EA major scheme were not satisfactory options.

Salisbury Cathedral

  • Commence public consultation on the four “Defend” options identified. Each have benefits, negatives and variable costs.
  • Consider a more detailed flood report review of the Cathedral and / or the Cathedral School.
  • Review all private foul drainage, such as soil vent pipes and back inlet gullies, with the aim of eliminating flow into the sewers even when external ground is flooded.
  • Identify a flood warner and emergency procedure and provide point of contact with the Authorities.
  • To start a process of consultation with the property insurers as regards putting in place a financial contribution towards the risk reduction benefit offered by the scheme.
  • To commence an informal review of land ownership and consent in principle for the work.

This report makes a wide range of recommendations to the various Authorities as to how they can play their part is identifying and mitigating flooding risks as follows:

Wessex Water:

  • Review the risk of covers lifting or infiltration through the covers within the study area.
  • Review the pumping station vulnerability to flooding, including security of electrical supply and risk of the wet well flooding.
  • To CCTV the Bishop’s ditch culvert and review capacity, levels and condition, with reference to option 2c and 2d.

Environment Agency:

  • Install borehole monitoring station to inform a long term groundwater strategy in Salisbury and provide early warning of groundwater related flooding to the public.
  • Improve the river station monitoring data output to aid the public.
  • Produce a professional review of viable upstream catchment management as set out by the Hampshire Avon Catchment Flood Management Plan.
  • Review the proposals and identify funding mechanisms to support this community led flood reduction project.
  • Consider the potential of adoption of flood reduction measures formally following construction.

Wiltshire Council:

  • Survey and assessment by the Council of its highway drainage assets, in areas where the Environment Agency has identified a high risk of flooding. This is needed to inform the emergency flood response coordination.
  • As Land Drainage Authority to formally request the Highway Agency review their structure.
  • To identify public funding to support this community led flood mitigation project.

Salisbury City Council:

Local community engagement will be essential to the project success. A defence is only as strong as the weakest link.

  • It is proposed that Salisbury City Council could provide considerable support in terms of public consultation.

Highway Agency:

  • A hydraulic flood risk review of their structure with reference to the existing limitations to capacity, to show compliance with the Land Drainage Act.

The recommended next stage was for the “Defend” options to be reviewed in more detail and initial designs produced for pricing. Funding should then be applied for from the Authorities, insurance industry and any other sources of public and private funding, as recommended by the Government.

Wilsham Consulting is has unique experience of working with Cathedrals, National Trust and advising clients with Grade 1 and Grade 2 listed buildings and estates, as to their flood risk from all the applicable flood mechanisms and the advancement of practical, but discrete, flood mitigation measures.

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